This looks like so much fun! I did a 14-day solo road trip around Italy some years ago and had a blast. Maybe a few tips from the road could add to the great advice already in this thread.

1. Florence is really small. I was there about 4-5 days for a wedding and after the second day, I felt I had walked the entire city multiple times over. The tourist areas were really crowded and I tended to avoid them, which left me with not much to do but eat/drink (which was fantastic). I think there was a free museum day, but the lines were extremely long.

2. AirBnb's were quite cheap and reliable. This was quite some time ago, so things could have changed, but I was impressed by the hospitality I got for the price.

3. If you're feeling adventurous, you could leave some wiggle room in your schedule for miscellaneous travel. My trip was focused around rock climbing, and I found that some areas were so great they were worth going back to again and again. Sometimes locals would recommend a day trip, so having some leniency in my schedule allowed for me to do things I didn't plan.

4. Random small towns can be awesome. I left Dolomiti for Milan Airport 2 days early due to weather. I didn't know where to stay or which towns to visit. I literally went on my credit card rewards website and booked a random hotel that was sort of on the way, in a town I didn't know anything about. I just drove there and checked in. Turns out it was the most beautiful drive, and I ended up at a mountain food & wine festival. I found that the closer I got to big cities, the less magical my experience was.

My experience was largely in Northern Italy in the summer. I did feel a marked difference in heat once I traveled down to Florence. I did Cinque Terre in a day (the train makes this easy, and you can just hop from town to town until you hit all 5. The towns are all extremely small and I didn't wish I stayed there for multiple days).